Field of the Invention
The present invention relates to an image forming apparatus in an electrophotographic system.
Description of the Related Art
In an image forming apparatus in an electrophotographic system, a laser light quantity of a scanner which is an exposing unit by which a photosensitive drum is exposed to laser light (hereinafter, laser light quantity) is changed in order to cope with aged deterioration of a member for image formation such as the photosensitive drum, which is caused by being used, in some cases. Moreover, for electrically collecting charged (positively charged or negatively charged) toner into a residual toner container used for the desired photosensitive drum (hereinafter, electrostatic cleaning), the laser light quantity may be switched to thereby adjust potential of the photosensitive drum. As above, it is necessary to enable correct acquisition of a BD signal regardless of the laser light quantity so that the laser light is correctly emitted even in a configuration in which the laser light quantity is changed.
Then, in Japanese Patent No. 3461257, proposed is a configuration of a circuit which acquires a BD signal from a scanner laser, in which a peak of a current passing through a BD signal acquiring circuit is held. In this configuration, a slice level corresponding to a fluctuation of a laser light quantity is set by a circuit which changes the slice level according to the laser light quantity.
However, in a configuration in which a peak hold circuit is used as the BD signal acquiring circuit, when switching a state of a laser light quantity from a large state to a small state, a discharge time of a peak hold capacitor of the peak hold circuit becomes longer than a laser light quantity switching time in some cases. In this case, when the slice level is greater than the laser light quantity in a period during which the slice level shifts to a level suitable for a small laser light quantity, it is difficult to acquire a BD signal. When the BD signal becomes unable to be acquired, there is a case where it is difficult to emit laser light at a suitable timing. In addition, rotation control of a polygon mirror is not controlled suitably and rotation speed becomes out of target, so that it takes long time to acquire the BD signal again and return the rotation to be regular rotation again. As a result thereof, a time required to start image formation becomes long in some cases.